The invention relates to an extraction valve head for a tank containing high-purity and/or toxic liquid chemicals, having an inlet valve for a filler gas, which connects a gas inlet line to a tank inlet, and an outlet valve, which connects a tank outlet to an extraction line, a bypass, which can be shut off by a purging valve, connecting the gas inlet line to the extraction line.
Tanks of steel, glass, plastic or similar materials are used for the transportation and the application of high-purity and/or toxic process chemicals. These tanks are provided with shut-off valves, which allow filling and extraction of the chemicals. These valves may be combined in an extraction valve head, which is fitted onto the tank.
Usually, the tank is fed via the gas inlet line with a filler gas, which serves to discharge liquid chemicals from the tank. The filler gas is fed either on the upper side of the tank and forces the liquid chemical through riser through the tank outlet into the extraction line or is fed via the riser extending into the liquid and takes portions of the liquid with it as it bubbles up.
It is known to purge the connected lines with a purging gas, for example the filter gas is also used for the extraction. In this approach, after closing of the inlet valve and the outlet valve, a bypass, which can be shut off by a purging valve, is opened, so that the gas can flow out of the gas inlet line into the extraction line. However, in this case unpurged dead spaces remain in the region of the inlet valve and the outlet valve.
Three-way cocks may be used as valves, in which channels which cannot be purged remain in the bores of the cock plug. In addition, with these cocks, no adequate, purely mechanical sealing is possible, as is necessary in the case of many such chemicals. Therefore, diaphragm valves are used for this purpose, in which a metal diaphragm ensures complete metallic sealing of the moveable valve parts with respect to the valve housing. However, in each case the diaphragm valves are only shut-off valves. In the purging operation, there remain in the line branches leading to the shut-off valves, unpurged dead spaces, which can only be purged by separate purging connections.